\begin{tikzpicture}
    \tkzDefPoints{0/0/B, 3/0/C, 2/2/A}
    \tkzLabelPoints[above](A)
    \tkzLabelPoints[left](B)
    \tkzLabelPoints[right](C)

    % 1
    \tkzDefLine[mediator, K=.5](A,B)  \tkzGetPoints{E}{D}
    \tkzCompasss(A,D  B,D  A,E  B,E)
    \tkzDrawSegments(A,B  D,E)
    \tkzLabelPoints[above right](D,E)

    % 2
    \tkzDefLine[mediator, K=.5](B,C)  \tkzGetPoints{F}{G}
    \tkzInterLL(D,E)(F,G)  \tkzGetPoint{O}
    \tkzCompasss(B,F  C,F  B,G  C,G)
    \tkzDrawSegments(B,C  F,G)
    \tkzDrawPoint(O)
    \tkzLabelPoints[right](F)
    \tkzLabelPoints[below](G)
    \tkzLabelPoints[below left](O)

    % 3
    \tkzDrawCircle[thick](O,B)

    % ex
    \tkzDrawSegment(A,C)
\end{tikzpicture}

